Transparent Nano Crystalline Glass‐Ceramics by Interface Controlled Crystallization

Abstract

A prerequisite for the preparation of nano glass‐ceramics is an increase in viscosity of the residual glassy matrix phase during the course of the crystallization process. This results in a deceleration of the crystal growth process due to increasing stresses, which finally may lead to a total freezing of the crystallization process. In principle, two routes for the preparation of nano glass‐ceramics exist: in one of these routes, the first step is a phase separation in which a droplet phase is formed. Inside this droplet phase, the crystals are precipitated. In the other route, a preceding phase separation does not occur and the nucleation takes place in a homogeneous glassy phase. In both cases, the crystal growth velocity is high until the crystals reach a size of some nanometers or some ten nanometers, then the crystal growth velocity decreases strongly.

Microstructure of Transparent Strontium Fresnoite Glass-Ceramics

“…On the other hand, the TEM-micrographs of this microstructure1921 show that the crystal domains are also very small. Hence it seems quite possible that the transparency observed here is initially similar to the transparency of glass-ceramics where the crystallite size is specifically controlled31. During subsequent annealing the samples stay transparent for a time because the SiO 2 agglomerates in the form of very thin grain boundaries between crystal domains in the μm-scale, perhaps similar to those observed in Sr 3 Al 2 O 6 ceramics crystallized from glasses32.…”

Crystallization, Microstructure, and Viscosity Evolutions in Lithium Aluminosilicate Glass-Ceramics

“…1997a; Kim et al, 2004;Fernandes et al, 2008;Wang et al, 2010;Lilensten et al, 2014). Recently, high-temperature X-ray diffraction (HTXRD) and anomalous small-angle X-ray scattering (ASAXS) have been utilized for the in situ observation of the phase transition and structural changes during hightemperature heat treatment (Misture, 2003;Holand et al, 2006;Sinton et al, 2008;Dressler et al, 2011b;Bocker et al, 2013;Lilensten et al, 2014;Raghuwanshi et al, 2014;Kleebusch et al, 2016). Despite the comprehensive understanding of the crystallization mechanism and microstructural changes, the viscosity evolution during the crystallization process remained unclear.…”

Self‐Organized Growth of Sodium Borate‐Rich Droplets in a Phase‐Separated Sodium Borosilicate Glass

“…This has been shown for the crystallization of alkaline earth fluorides (CaF 2 SrF 2 , and BaF 2 ), KZnF 3 as well as high‐quartz solid solutions . The silica‐enriched layer around the growing crystals has been proved by electron energy loss spectroscopy (EELS) as well as by anomalous small angle X‐ray scattering (ASAXS) . Also in these cases, a strong deceleration of crystal growth with time has been observed.…”